In recent years, a progress of integration of microwave circuits has involved demands for a dielectric resonator having a small size, less dielectric loss (tan δ), and stable dielectric characteristics. There hence has been a growing market of laminated chip parts internally having laminated electrode conductors for dielectric resonator parts. Inner conductors of these laminated chip parts have been using noble metal such as Au, Pt, Pd, or the like. From the view point of cost reduction, however, conductor materials have been replaced with Ag or Cu or alloy containing, as a major component, Ag or Cu, which is relatively cheaper than the conductor materials described above. Particularly, Ag or alloy containing Ag as a major component is strongly demanded, since it has a low resistance to a direct current and therefore is advantageous for improvement in the Q-characteristic of the dielectric resonator, etc. However, Ag or alloy containing Ag as a major component has a low melting point of about 960° C. and necessitates a dielectric material which can be sintered at a temperature lower than the melting point.
In case of forming a dielectric filter with use of a dielectric resonator, characteristics which are requested for a dielectric material are: (1) a small absolute value of the temperature coefficient τf of the resonant frequency of a dielectric material to reduce, as much as possible, characteristic changes caused by temperature changes; and (2) a high Q-value of a dielectric material to reduce insertion loss, as much as possible, as requested for a dielectric filter. Further, with respect to a range near a micro wave used by a cellular phone or the like, the length of a resonator is limited by a relative dielectric constant εr of the dielectric material. Therefore, a high relative dielectric constant εr is requested for downsizing of elements. In this case, the length of the resonator is determined with reference to the wavelength of a used electromagnetic wave. The wavelength λ of the electromagnetic wave propagating through a dielectric material having a relative dielectric constant εr is expressed by λ=λ0/(εr)1/2 wherein the wavelength of the electromagnetic wave propagating through vacuum is λ0.
Accordingly, elements can be downsized more as the dielectric constant of the dielectric material used increases. However, if the element is too small, required processing accuracy is severe. Therefore, actual processing accuracy deteriorates and is easily affected by printing accuracy of electrodes. For some purposes, the relative dielectric constant εr is required to be within a proper range (e.g., about 10 to 40 or more preferably about 15 to 25) so that elements might not be too small.
To satisfy these requirements, known dielectric materials capable of preparing a dielectric member at a temperature not higher than 1000° C. may be a material in which inorganic dielectric particles are dispersed in resin (JP(A)-6-132621), glass ceramics consisting of a composite material of BaO—TiO2—Nd2O3-based ceramics and glass (JP(A)-10-330161, page 3, paragraph [0005] and Table 1), and the like. Also known is a dielectric ceramics which contain TiO2 and ZnO and further contain B2O3-based glass (JP(B)-3103296).
However, the element disclosed in the JP(A)-6-132621 has an allowable temperature limit of about 400° C. and causes a problem that multi-lamination and fine wiring cannot be carried out by simultaneous sintering with Ag or the like used as a wiring conductor.
The glass ceramics material disclosed in JP(A)-10-330161 has a problem as follows. The relative dielectric constant εr of this material is greater than 40 so that the element becomes too small. Consequently, required processing accuracy is so severe that actual processing accuracy deteriorates and is easily affected by printing accuracy of electrodes.
Further, the composition disclosed in the JP(B)-3103296 has a relative dielectric constant εr as high as about 25 to 70, as can be seen from Examples. The temperature coefficient of a dielectric characteristic varies greatly by the composition, so that the absolute value thereof exceeds 700 ppm/° C. in some cases. In order to provide a dielectric part for a high frequency, such a material has been demanded that has a proper relative dielectric constant, a small dependency of the dielectric characteristic on temperature, and a high Q-value.
Further, the dielectric characteristic of dielectric ceramics obtained by sintering a dielectric ceramic composition usually changes or has variants due to changes in sintering temperature and in composition. These changes and variants of the characteristic due to changes in sintering temperature and in composition cause deterioration of the yield in mass production.